1. Field of the Invention
The present invention relates to a sleep warning apparatus.
2. Description of Related Art
Conventionally, for example, JP-A-S56-2227, JP-A-H6-197888 (corresponding to U.S. Pat. No. 5,574,641), and JP-A-H11-189066 describes a falling-asleep-at-the-wheel warning apparatus for preventing a driver from falling asleep at the wheel. The falling-asleep-at-the-wheel warning apparatus described in JP-A-S56-2227 generates a pre-warning when a monotonous drive is detected. If the driver performs an operation of pressing a reset switch in response to the pre-warning, a warning (main warning) is not generated. However, if the above response operation is not performed, the main warning is generated.
The sleepiness of the driver depends on an individual difference, a body condition, and a psychological state, and therefore, the estimation result of the sleepiness does not always match with subjectivity of the driver. As a result, in a case, where the warning is generated based on the above estimation result, the warning may be generated when the sleepiness progresses to a certain extent to a certain driver, and thereby timing for providing the warning may be too late. In other case, the warning may be annoying the driver when the warning is given to the driver while the driver is aware. Therefore, as described in JP-A-S56-2227, the pre-warning is generated before the main warning is generated such that the main warning is not generated if the driver performs the response operation to the pre-warning. As a result, an unnecessary main warning is limited from being generated.
However, because the pre-warning may be generated while the driver is awake similarly to the main warning, a pre-warning that is not annoying to the driver is needed. Also, in the above JP-A-S56-2227, because the response operation needs to be performed every time the monotonous drive is detected, the driver may feel troublesome in performing the response operation.